1. Field of the Invention
The present invention relates to charged particle beam equipment for scanning a charged particle beam over a specimen, and forming an image by using a signal generated when the specimen is irradiated by a charged particle beam.
2. Description of the Related Art
Heretofore, with charged particle beam equipment, such as a scanning electron microscope, a focused ion beam observation device, and a transmission electron microscope, when calibrating a magnification and a measured length of images accurately, is has been a usual practice to measure an interval dimension representing the feature of a specimen by using a microscale specimen whose dimension is known, or using scanning a secondary-electron image or a scanning transmitted electron image of crystal lattice. As a conventional technology for calibrating a display magnification by using a standard specimen, there is a technology revealed in JP-A-2002-15691. In JP-A-2002-15691, a specimen is not specified, but it is stated that when the acceleration speed or the working distance changed in a scanning electron microscope, by measuring a change in magnification, the display magnification or the scale bar is calibrated.
FIG. 2A is an enlarged view of a microscale specimen, which is generally available in the market, and in which the pitch distance is 0.24 μm. FIG. 2B is a crystal fringe image of a gold single crystal thin-film specimen, in which the lattices with a crystal lattice spacing of 0.204 nm intersect with one another. For example, to use a gold single crystal thin-film specimen as a dimensional standard, it is necessary to take an enlarged image of a specimen at a magnification at which crystal lattice images of gold can be observed, and to enlarge a lattice image with of an interval of 0.204 nm to an interval of 1 mm, it is necessary to multiply 0.204 nm by a magnification of 5000×103. Under an actual scanning transmitted electron microscope, to make this lattice image large enough to recognize lattices in the image, it is necessary to provide a magnifying power of not less than 3000×103. Calibration of an observation magnification or a measured length by using a lattice fringe image proceeds as follows at a magnification used in photographing. Suppose that the magnification (display magnification) displayed on the electron microscope was 3000×103, and when a gold single crystal specimen with a crystal lattice spacing of 0.204 nm was photographed, and the lattice interval displayed was 0.62 mm, the true magnification at this time can be obtained as:0.62 mm/0.204 nm=3039.22×103.
In other words, the display magnification includes an error of 1.31%. Similarly, the dimension (measured length) between two points in an image taken at this display magnification was displayed 1.31% larger than it actually is.